1. Field of the Invention
The present invention relates to a wire bonder which performs assembly of semiconductor integrated circuits (IC), etc., and more particularly, relates to a wire bonder and wire bonding method which are able to linearly connect wire between a pad (electrode) of a semiconductor pellet (IC pellet) and a lead arranged on a lead frame.
2. Description of the Prior Art
With respect to the prior art, in the case of manufacturing semiconductor integrated circuits (IC) or large-scale integrated circuits (LSI), by displacing a bonding tool (capillary) holding a wire with respect to a lead frame and an IC pellet, after positioning said lead frame on which said IC pellet is arranged on a conveyor device, bonding is performed by respectively guiding the wire to a lead arranged on said lead frame and a pad on said IC pellet. A wire bonder like that indicated in FIG. 1 is used for this type of bonding.
In FIG. 1, the bonding head is comprised of ultrasonic vibrator 10, supported to allow oscillation (up and down movement) by means of support shaft 13 provided on frame 12 provided on XY table 11, which is capable of moving two-dimensionally in the X and Y directions; bonding arm 14 provided on the end of said ultrasonic vibrator 10; capillary 22 mounted on the end of said bonding arm 14, lever 15 mounted on the other end of ultrasonic vibrator lo, and roller 16 provided on the end of said lever 15.
Roller 16 is comprised so as to receive a moment in the counterclockwise direction from spring 18 so as to make contact with cam 17. As a result of cam 17 being rotated by a driving device such as a pulse motor, capillary 22 is able to move up and down in an oscillating fashion due to the shape of said cam 17. In addition, wire 4, made of aluminum or gold, is wound about rotatable supply reel 19 on a support frame on XY table 11. The wire 4 is pulled out to a specified length from the end of capillary 22 by means of half clamp 20 and clamp 21.
The following describes the procedure by which bonding work is performed using the device comprised as mentioned above.
Firstly, a specified length of wire 4 is extended from the end of capillary 22. After forming a ball (not shown) on the end of wire 4 with a torch (an electric discharge device not shown), capillary 22 is positioned at a location directly above pad 3 formed on IC pellet 2 placed on bonding stage 1 by moving XY table 11.
Next, capillary 22 is lowered by rotating cam 17. The ball formed on the end of capillary 22 is brought in contact with pad 3 on IC pellet 2 to crush the ball resulting in connection at the first bonding point. Simultaneous to this crushing, ultrasonic vibrator 10 is operated to subject capillary 22 to ultrasonic vibration, and bonding stage 1 is heated by means of a heating device (not shown). Then, after capillary 22 is moved upwards and horizontally to position it above the lead to be bonded, capillary 22 is lowered to partially crush wire 4. This results in the formation of a flattened portion which makes a connection at the second bonding point as a result of being fixed to the lead through the combined use of ultrasonic vibration and heating. Wire 4 is then pulled back and cut from the edge of the flattened portion. One round of bonding is thus completed with the raising of the capillary. In the connection of wire 4 by means of the wire bonding procedure described above, since wire 4 forms a wire loop as indicated by the broken line in FIG. 4(A), it follows that pad 3, the first bonding point, and lead 5, the second bonding point, are nominally connected by a straight line.
In the wire bonder of the prior art, however, although capillary 22 moves in the Z (upward) direction when bonding arm 14 oscillates by angle 0 around support shaft 13 as the center of rotation, since the end of capillary 22 moves in the form of a circular arc about the pivot point 13 during said oscillating motion, bonding arm 14 ends up being dislocated horizontally by the amount dy in the direction of axis Y--Y' (see FIG. 2) As dislocation dy becomes larger in proportion to angle .theta. (angle .theta. is not constant), when bonding is performed with lead 5 as the second bonding point by moving XY table 11 two-dimensionally in the X and Y directions while still in this dislocated state, the end of capillary 22 does not follow a linear path, but rather follows an arcuate path. Consequently, this results in a curved wire being extended between the two bonding points as indicated in FIG. 4(A). Thus, the prior art has the disadvantage that curved wire 4 may make contact with an adjacent wire 4, resulting in the risk of the occurrence of broken wires and other problems contributing to defective bonding.